1. Field of the Invention
The invention relates to a clutch disk for a friction clutch, especially for internal combustion engines. Such a clutch disk has a hub, two friction disks connected with the hub so as to be concentric thereto, and a plurality of facing spring elements which are connected with the friction disks so as to be rotatably fixed relative to them. The spring elements are provided between the friction disks in the circumferential direction. The facing spring elements are also bent or curved in a wavy manner and nested or braced against one another in pairs so that they exert a force on the friction disks in the axial direction.
2. Discussion of the Prior Art
A clutch disk of this kind is known, for example, from German patent 21 11 892. During the process of engaging the clutch, the pressing plate of the clutch, in conjunction with the flywheel of the internal combustion engine acting as counter-pressure plate, exerts a force on the friction clutch for transmitting torque. The spring elements which are arranged between the friction disks and which, taken together, likewise form a ring, permit the axial movement of the friction disks. Consequently, the torque is transmitted from the flywheel to the pressing plate in a gradual build-up instead of a non-uniform or jerky fashion, resulting in improved start-up driving comfort. Further, vibrations can be damped so that they are not transmitted in their entirety to the power train. To allow this damping, the spring elements are designed so that a residual spring path is maintained while the clutch is engaged and the spring elements do not rest perfectly flat against the friction disks.
When not loaded, the spring elements which are arranged opposite one another abut at their ends on their circumferencial sides. Because of the wavy shape of the facing spring elements, which does not completely disappear even in the loaded state, the contact surface on the back of the facing is naturally small. Facing wear and spring relaxation or spring set can therefore not be optimal. The area pressure in the spring elements and on the back of the facing is correspondingly high. When residual springiness is deficient, squealing--a high-pitched squeaking or whistling noise - occurs and, with the increasing trend toward minimizing driving noise, is distinctly audible to the occupants of the vehicle. A further result of high area pressure is the risk of increased wear on the back of the facing and losses due to spring set. Furthermore, the contacting ends can rub against each other causing wear and noise.
The spring elements are riveted to a disk body by their feet which project inward radially over the friction facing disks. The disk bodies are fastened, in turn, to the hub. This foot must have no waviness if a secure fastening is to be possible. For this reason, the quantity of waves in the known spring elements is limited. In order to increase the height of the waves, it is known to separate the foot from the spring element by means of a slit located farther outside radially so that the spring element can also be wavy at the level of the foot, while the foot itself is flat. However, a slit of this kind in the area of transition to the foot is problematic as regards fatigue strength, since this can lead to higher stresses in the spring element. High-quality work materials must be used in order to compensate for this fatigue strength problem, a direct result of this being stricter requirements for the manufacturing tools, which increases production costs. Manufacturing problems also cannot be ruled out. Limiting or boundary designs would result in a drop in function in the facing spring characteristic.